Transactional Paths in the Reticular Activating System

Approximately one decade separates this symposium on Hallucinations from the previous one [29]. That period has been marked by several conceptual changes in our understanding of the role and organizational pattern of the brain stem reticular core; changes which include a realization of the essentially modular or mosaic nature of the system, its multimodal effects on the sleep-wakefulness pattern of the organism, the presence of acetylcholine and monoamine rich subsystems, the ease with which reticular elements habituate to iterative stimuli, and the apparent existence of cyclic sensitivity patterns measurable at the level of the single neuron. The plurimodal nature of operations in the reticular formation (r.f.) appears reflected at the level of the single cell where individual dendrites are largely devoted to single input systems and, perhaps, to specialized integrative operations.